A wood chipper in which waste veneer is made into chips, an elongate anvil, which coacts with a cutter, is bolted to an anvil base. However, because of the forces applied to the anvil, the bolts and the anvil become loose from the base and cause a considerable damage to the chipper and results in expensive repairs and expensive down time. Therefore, it becomes important to know when the bolts securing the anvil to the base become loose before damage occurs. Because of vibration and the high moisture, the usual mechanical and electronic sensors are not satisfactory.
The present invention is directed to a detector which is useful for supplying gas to the mating surfaces of two bolt held members and produces an alarm in the event that the bolts become loose and the surfaces separate to allow the gas to escape.